Method of pouring cast iron



June 16, 1964 .1. THlEME METHOD OF POURING CAST IRON 2 Sheets-Sheet 1Filed July 31, 196].

INVENTOPS Jack em 7Zieme June 16, 1964 J, THlEME 3,137,566

METHOD OF POURING CAST IRON Filed July 31, 1961 2 Sheets-Sheet 2 Fig.2

INVENTOPS Joabem 77ueme United States Patent 3,137,566 7 METHOD OFPOURING CAST IRON Jochem Thieme, Siegen, Westphalia, Germany, assignorto Kolsch-Folzer Werke Alttieugesellschaft, Siegen, Westphalia, GermanyFiled July 31, I961, Ser. No. 128,643 Claims priority, applicationGermany Aug. 2, 1960 Claims. (Cl. 75-56) The present invention relatesto a method of and apparatus for casting cast iron. In connection withsteel casting it is known to pass the liquid steel through a vaccum inorder to obtain a degasification and a separation of harmfulingredients.

According to a heretofore known apparatus for carrying out this method,an empty casting ladle is inserted into a vacuum container which istightly closed by a lid. A second casting ladle is then tightly placedupon the ladle of the vacuum container. The lid of the vacuum containerhas a passage for the liquid steel which passage is closed by adiaphragm. After the vacuum has been produced, the steel is poured in,whereby the diaphragm melts so that the steel will without loss in timeenter the vacuum chamber.

It has already been known in conformity with this known principle topass cast iron through a vacuum. In connection with this method, it wasfound that a reduction in the strength and the hardness of the pig ironoccurred. Numerous tests have proved that the strength is reduced by 20%and that the hardness is reduced by 13%. In this connection, referencemay be had to a paper delivered by Otto Nekas and Robert Kaminski, datedOctober 1959, and issued by Eisenwerke Vitkovice. In this paper a testhas been described concerning the passage of cast iron similar to theabove mentioned passage of cast steel, through a vacuum.

For the reasons described in the said paper, the casting art hasrefrained from treating cast iron in a vacuum because the reduction ofthe strength by 20% is prohibitive.

It is, therefore, an object of the present invention to provide a methodof and apparatus for casting cast iron, which will overcome the abovementioned drawbacks.

It is another object of this invention to provide a method of andapparatus for casting cast iron in connection with a vacuum treatmentthereof which will for all practical purposes not result in a reductionin the strength.

These and other objects and advantages of the invention will appear moreclearly from the following specification in connection with theaccompanying drawings, in which:

FIG. 1 illustrates a diagrammatic section through an apparatus forcarrying out the method according to the present invention.

FIG. 2 is a section through a modified apparatus according to thepresent invention.

General Arrangement The present invention is based on applicants findingthat the reduction in the strength of the cast iron by vacuum treatmentis caused by the reduction in the oxygen content of the melt. Theinventor was able to ascertain a reduction in the oxygen content from 40to 70%. The reduction in the strength of the cast iron depends on theseparation of the carbon dissolved in the melt which carbon separates inthe form of graphite during the solidification of the casting. Only ifthe carbon is separated in a certain form, the strength will be assured.This separation depends on the so-called nuclei. In connection withtechnical melting operations, only those foreign 3,137,566 Patented June16, 1964 nuclei are of importance which consist to the major extent ofsilicates or oxides, i.e. of metallic or non-metallic compounds withoxygen. Such oxygen compounds can be present only if suflicient oxygenis present. If, however, not sufficient nuclei of this type are present,subcooling and other mis-formations of graphite crystals will occurwhich will at any rate produce a reduction in the strength.

The lack in nuclei is also a result of the loss in oxygen which isproduced by the vacuum treatment of the melt because the melt due to theloss in oxygen loses its ability to form oxides.

From the above finding, the inventor drew the conclusion that the lackor low content in nuclei which is unavoidable during a vacuum processmust be remedied.

Therefore, according to the present invention, following thedegasification in a vacuum, the melt is again enriched with oxygen inorder thus to produce a favorable nucleus condition. In this way, thereduction in strength will be safely avoided.

The method according to the present invention was practiced by anapparatus according to the present invention in the following manner:

In a normal light are of from to kilograms capacity, the cast iron meltwas produced. The chargemay consist of pig iron, scrap, waste, andchips. The liquid melt was poured into a plug ladle (Stopfenpfanne) andin this ladle was tightly placed upon a vacuum container. By opening theplug, the iron was discharged while melting an aluminum foil between thevacuum container and the plug ladle which aluminum foil had previouslysealed the vacuum container. Thus, the iron passed into the vacuumchamber. The melt passes through the vacuum chamber in a free flow andis collected in a casting ladle mounted below the vacuum chamber in avacuum-tight container.

In order to assure that in conformity with the invention, following thedegasification in the vacuum, the cast iron will again be enriched withoxygen, it is possible in conformity with a special embodiment of theinvention, already prior to passing the melt through the vacuum, tointroduce a substance, which gives off oxygen, into the casting ladlebelow the vacuum chamber. Such substance may consist for instance ofscale or the like. Instead, also oxygen may be introduced into thecollecting ladle.

As numerous tests have proved, the cast iron again enriched in the abovementioned manner with oxygen will, following the degasification,maintain a sufiicie'ntly favorable nucleus condition and Will retain itsstrength.

In addition to the giving off of oxygen by means of which the melt isagain enriched after having passed through the vacuum, the melt willalso give off hydrogen and nitrogen. As a result thereof, a reduction inthe hardness will take place which, even after the enrichment withoxygen following the discharge from the vacuum, will be retained becausethe hardness is, in view of the gases, dependent on the carbidestabilizing effect and not on the oxygen content. In addition to theincreased strength of the cast iron in conformity with the methodaccording to the present invention, the hardness is reduced. This isfavorable because the construction of machines favors a soft easilymachinable cast iron with high strength.

A further advantage of the cast iron according to the present inventionconsists in that due to the reduction in hydrogen and nitrogen, thetendency to hard edges, bubbles and blow holes will be reduced.

Finally, due to the degasification in a vacuum, the heat conductivity ofthe cast iron is increased.

Above all, it is to be mentioned that it is the present invention whichfor the first time has made it possible to arazsee carry out thedegasification of the cast iron melt in a vacuum because the heretoforeknown method for treating steel casting in a vacuum could not beemployed for cast iron in View of the reduction in strength of the castiron.

Due to the increase in the heat conductivity of the cast iron which isobtained when melting in a vacuum, and which is a result of thedegasification in the vacuum, the density of the cast pieces isconsiderably increased. The conductivity of lamellar cast iron isincreased by the vacuum treatment, as found by the in ventors, up to25%. Thus, by means of the vacuum treatment, a cast iron with high heatconductivity may be produced which is better suited than ordinary castiron for thermically stressed cast pieces. This is extremely importantfor instance for molds of steel plants. The inventors found that thedurability of such molds is considerably affected by the heatconductivity thereof. Also when making grates, oven doors, cast ironshafts etc. the increase in the heat conductivity is of greatimportance.

If parts are involved for which the strength is of secondary importance,the enrichment with oxygen after passing the melt through the vacuummay, of course, be omitted.

The invention may also be employed for making cast iron with spheroidalgraphite. Cast iron with spheroidal graphite is produced in a mannerknown per se by adding magnesium to the melted liquid iron.

The particular advantage of this known method consists in that theemployed magnesium alloys are extremely inexpensive. For instance, whenmelting in acidic furnaces, of an alloy is employed which contains 15%magnesium and 85% nickel. A ton of such alloy costs approximately$2,500.00.

The present invention makes it possible considerably to reduce the costsof this rather expensive method. In this connection, it should be keptin mind that by the magnesium alloy the following will be obtained:

A portion of the sulphur present in the melt is removed while anotherportion binds the gases and more particularly oxygen and nitrogen. Afurther portion of the magnesium will have to remain in the iron insolved condition.

In conformity with the features of the present invention, the melt ispassed through a vacuum prior to the magnesium treatment.

As a result thereof, the oxygen and nitrogen will be removed from themelt and also a certain de-sulphurization (approximately 10%) will beobtained. The inventors have ascertained that due to the vacuumtreatment of the melt, approximately up to 40% of the magnesium alloywill be saved because the removal of oxygen and nitrogen and also of aportion of the de-sulphurization when passing the melt through thevacuum is already obtained and therefore no magnesium is required anylonger.

The decrease in costs which is obtained by the treatment of the melt inconformity with the present invention is very considerable. Moreover,the vacuum treatment of the cast iron with ball or spheroidal graphitehas a number of other advantages. The heat conductivity of the ironincreases by the vacuum treatment up to Due to the fact that thegraphite stabilized gases hydrogen and nitrogen are removed alreadyprior to the magnesium treatment, the cast iron with ball graphite incasting condition has a considerably greater toughness and considerablybetter strength properties which otherwise could be obtained only bytempering. As has been found out by the inventors, the expansibility incast condition increases up to 75% and the bendability up to 200%. Ithas been found that the bending product (product of bending strength andbending) at 80 to 100% spherolite formation increases by from 200 to500%.

Cast iron with ball graphite treated in conformity with the presentinvention does not produce any cementite, and the perlite component isreduced in favor of the ferrite component. According to the ordinarymethod, however, cementite is produced, and the perlite com ponent ishigh.

Referring now to the drawings in detail, the apparatus illustrated inFIG. 1 has a vacuum container 1 provided with a lid 2 at its upper end.Lid 2 and vacuum container 1 are by means of flanges 3 and an interposedseal 25 connected in an air-tight manner, for instance by bolts notshown in the drawing.

Lid 2 has an opening 4 with an outwardly extending connection 5 forconnection with a vacuum pump 26 by means of which a vacuum may beproduced and main tained in the vacuum container 1.

Furthermore, lid 2 is provided with a second seal 6 substantiallycentrally located in lid 2. Extending through this seal in an air-tightmanner is a discharge connection 7 of a plug ladle 8. The dischargeconnection 7 is by means of a flange 9 fixedly connected to a connection11 which is arranged below the bottom 10 of the plug ladle 8 and extendsdownwardly. Between the flanges 9 and discharge connection 7 there isclamped an aluminum foil 18 or a foil of another easily meltablematerial which closes the discharge passage 12 in an air-tight manner sothat after the plug ladle has been placed upon lid 2 of the vacuumcontainer 1, no air Will be able to enter the interior of the vacuumcontainer.

The discharge opening 13 of the plug ladle 8 may be closed by means of aplug 14. For purposes of withdrawing and inserting said plug 14 there isprovided a gripper member 15 or the like. Arranged in the interior ofthe vacuum container 1 is a casting ladle 16. This ladle is so arrangedthat it rests in the vacuum container substantially vertically below themouth of the discharge connection 7. The arrangement of the castingladle in the interior of the container 1 has the advantage that noseparate seal Will be required for connecting the casting ladle to thecontainer. It is, of course, also possible to connect the casting ladlein an air-tight manner by means of a seal to the bottom side of anopening in the bottom of container 1.

In order to assure that following the degasification, oxygen will againbe introduced into the cast iron, the arrangement with the apparatusaccording to FIG. 1 is such that when inserting the casting ladle intothe vacuum container 1, a substance 17, as for instance scale, adaptedto give off oxygen is introduced into the casting ladle.

The apparatus illustrated in FIG. 1 operates in the following manner:

The casting ladle is inserted into the vacuum container 1, and thesubstance 17 adapted to give olf oxygen is introduced into the castingladle 16. Thereupon, lid 2 is connected to container 1 by means offlange 3 and by interposing a seal or gasket 25.

Depending on the local conditions, the plug ladle 8 is first placed onlid 2 of the vacuum container 1 and then is filled with molten castiron. However, it may also be filled at another station and then placedu on lid 2. At any rate, prior to filling the plug ladle 8, thedischarge opening 13 in the bottom 16 of the plug ladle is closed byplug 14 by means of the gripper member 15.

After the ladle has been filled and placed upon the lid 2 of the vacuumcontainer 1, first by means of the vacuum pump 26 the required vacuum isproduced in container 1. Then plug 14 of plug ladle 8 is lifted by meansof i the gripper member 15. The cast iron melt Will then free space ofthe vacuum container 1, the cast iron melt will be degasified by theinfluence of the vacuum. As soon as the said melt enters the castingladle, oxygen will be given off by the substance 17 to the melt so thatthe melt will be enriched with oxygen. As a result thereof, the castiron will, following its degasification, obtain a favorable nucleuscondition and will thus retain its strength.

Referring now to FIG. 2, the apparatus illustrated therein for carryingout the method according to the present invention corresponds to a greatextent to the device according to FIG. 1. Similar parts have, therefore,been designated with the same reference numerals as in FIG. 1 but havebeen primed, so that a description of these parts would appear to besuperfluous.

The apparatus according to FIG. 2 differs from that of FIG. 1 primarilyin that no substance giving oif oxygen is introduced into the castingladle 16. Instead, during or following the filling with the cast ironmelt, oxygen or an oxygen containing gas is introduced into the meltwhich is in the casting ladle 16. To this end, the wall of the vacuumcontainer 1' is connected to a source of oxygen not shown in thedrawing. Into the interior of the vacuum container 1' there isintroduced a gas conduit 20 which leads into the casting ladle 16 andhas its mouth spaced from the upper level of themelt relatively slightlyso that a goo-d intermixing effect of the entire cast iron melt in theinterior of the ladle with oxygen will be assured. The oxygen may beblown through conduit 20 into the cast iron melt in the interior of theladle 16. However, it is also possible to draw oxygen through the bathof the melt by means of a vacuum pump (not shown) connected to theconnection 5'.

Advantageously, the feeding of oxygen is effected following the fillingof the casting ladle 16' with cast iron. However, it may also beeffected already during the filling operation. In this connection,however, it should be borne in mind that in spite of the feeding ofoxygen into the interior of the vacuum container, a sufiicientvacuummust be maintained. In other respects, the apparatus according to FIG. 2operates in the same manner as that described above in connection withFIG. 1.

It is, of course, to be understood that the present invention is, by nomeans, limited to the particular constructions shown in the drawings butalso comprises any modifications within the scope of the appendedclaims.

What I claim is:

1. In a method of casting cast iron, the steps of: passing the cast ironmelt through a vacuum, and subsequently enriching said melt with oxygen.I

2. A method according to claim 1, which includes th step of enrichingthe melt with oxygen by introducing oxy- 'gen in gaseous form into saidmelt.

3. In a method of casting cast iron, the steps of: passing the cast ironmelt through a vacuum, and subsequently intermixing said melt with asubstance adapted in contact therewith to free oxygen for absorption bysaid melt.

4. In a method of casting cast iron, the steps of: passing the cast ironmelt in a free flow through a vacuum chamber, subsequently collectingsaid molten cast iron in a ladle and introducing into said ladle asubstance adapted to free oxygen when contacting the molten iron in saidladle.

5. A method of making cast iron with spheroidal graphite, which includesthe steps of: passing the cast iron melt through a vacuum, andsubsequently adding magnesium to said cast iron melt.

References Cited inthe file of this patent (Corresponding British Patent852,424 for patent in English language)

1. IN A METHOD OF CASTING IRON, THE STEPS OF: PASSING THE CAST IRON MELT THROUGH A VACUUM, AND SUBSEQUENTLY ENRICHING SAID MELT WITH OXYGEN. 